The objectives of the proposed research are to characterize the cytoskeleton, more specifically the microtrabecular lattice (MTL), in normal and cancer cells, and to characterize the ultrastructure of reconstructed actin gels in vitro. All normal eukaryotic cells are known from their form and internal morphology to be nonrandomly organized. This nonrandom organization is reflected in the disposition of the membrane-bound systems (e.g., the endoplasmic reticulum), the membrane-bound organelles (e.g., lysosomes, mitochondria), and in the cytoskeleton (e.g., microtubules, actin microfilaments, intermediate-size microfilaments). It is accepted now that components of the cytoplasmic ground substance are structured and are considered to be integral parts of the totally organized cytoplast characteristic of normal eukaryotic cells. In addition, it is now thought that actin (both G- and F-forms) is a major component of the MTL, although its form and distribution remains largely unknown. Techniques developed in our laboratory can visualize these components of the cytoplasmic ground substance with excellent resolution. Thus by examination of normal and cancer cells in culture, and normal and tumor cells in situ, by our ultrastructural methodologies, we will determine if the observed differences in the cytoskeleton of cancer cells are reflected also in the disposition of the microtrabecular lattice.